34 THE VITALITY AND GERMINATION OF SEEDS. 



cabbage, carrot, and lettuce germinated only 1, 2,5, and 1 per cent, 

 respective!}". 



During the succeeding 00 days nuich mold had developed, and at 

 the expiration of the experiment, 140 days, onh' the carrot and the 

 lettuce gave any indications of vitality. It is especially interesting to 

 note with what rapidity the deterioration took place between the sixty- 

 ninth and the eighty-first da^^s, shoAving that when vitality reaches a 

 certain point in its decline there follows a comparatively sudden 

 death. This same fact is also shown in the case of those seeds in this 

 same series kept at the higher temperature. After 31 days' treatment 

 they all failed to germinate, except 0.5 per cent in carrot and 2 per 

 cent in lettuce seeds. 



Jn the two series of experiments just considered there was an increase 

 in water content as a result of the humidity of the air in which the 

 seeds were kept. But the third series, <)j:)en and dry^ presents quite 

 another factor. A weighing made at the end of 30 days showed that 

 there had been an average loss of 2.5 per cent for the lower tempera- 

 tures and 3.5 per cent for higher temperatures. After this time the 

 weight remained nearly constant. Subsequent experiments, which 

 will be considered later, also show that the water capable of being 

 expelled at any given atmospheric temperature is driven ofl' in a com- 

 parativel}^ short time. In case of seeds this condition is pi'actically 

 comijleted in eight or ten days when maintained at temperatures as 

 above given. This extra drying of the seed causes a greater contrac- 

 tion of the seed coats, and in a number of cases a corresponding- 

 retardation in the rapidity with which germination takes place. The 

 retardation in the germinative activit}' is dependent on the increased 

 difficulty with which the seeds absorb water, and in many cases has an 

 important bearing on the vitality tests. 



■ The fourth and last series, in which the air-dried seeds were sealed 

 in bottles and subjected to the temperatures at which the two o\ens 

 were maintained, gave still another very different set of conditions. 

 Here there was also an increase in weight, due probably to some 

 process of oxidation, but the increase was very slight. The average 

 increase from those kept at either of the temperatures was less than 

 one-half of one per cent. 



Seeds, if well matured and thoroughly air-dried, arc not injured 

 when kept at temperatures below 37'-' C, whether they be kept in free 

 communication with fresh air, or in sealed bottles, or tubes. In the 

 experiments under discussion the average percentage of germination 

 was slightly higher in the case of the seeds which had been stored in 

 the sealed bottles. The mean percentage of germination for the seeds 

 which had been exposed to the open air at a temperature of 30° to 

 32° C. was 83.05 per cent. Those from the sealed bottles kept at the 

 same temperature germinated 84.82 per cent. At the higher temper- 

 atures — 36° to 37° C. — the mean germination of the seeds from the open 



